The present invention relates to apparatus for stripping the insulation from a segment of indeterminate length wire, and in particular to the use of such apparatus in connection with machines for forming stator coils.
In the manufacture of electric motors and other dynamoelectric machines, the excitation windings are usually made of magnet wire comprising a copper or aluminum core covered with a suitable layer of insulation, which may comprise a very thin coating of varnish or polyester resin. The wire is fed into the winding machine, formed into coils, as by the wind and shed technique, for example, and inserted into the slots of the stator core. Winding machinery of the wind and shed type is well known, and is described in the following exemplary U.S. Pat. Nos., which are expressly incorporated herein by reference: Lauer et al. 3,977,444; Arnold et al. Re. 29,007; Cutler et al. 3,672,026; Arnold 3,672,027; Cutler et al. Re. 27,415; Smith 3,510,939; Lauer 3,765,080; Lauer 3,579,791; Smith 3,514,837; Arnold et al. 3,973,601; and Arnold 3,967,658.
During or after the winding process, the wire is cut at one or more places so as to produce a plurality of free ends. The wire ends are connected to a lead set, other motor windings, or terminal devices. Before the connections can be made, however, it is necessary to remove the insulation from the wire. In the past, one technique for removing the insulation was that of brazing wherein the operators would twist the wire ends around whatever they were to be connected and then heat them with a small torch, at the same time touching the heated wire and other wire or connection device with silver solder. The torch would burn away the insulation, while at the same time melting the solder so that a good solder connection was established. As electric motor technology has become more sophisticated, however, insulations have been developed which can withstand much higher temperatures, even exceeding the temperature produced by the torch. As a result, the copper or aluminum core of the wire is melted before the insulation so that all that remains is a very fine tubular segment of insulation having no conductive material therein. Obviously, this prevents the establishment of electrical conduction between the wire and the connection device.
Another prior art technique for making electrical connections to the wire ends is to utilize crimp connection devices, which pierce the insulation and make contact with the conductive core of the wire. Examples of this technique are disclosed in U.S. Pat. Nos. 3,505,720 (Heimbrock) and 3,962,780 (Kindig). There have been substantial problems of reliability with crimp connection devices, however, particularly in demanding applications wherein it is necessary for the connections to maintain very good conductivity over a long period of time.
In order to avoid the reliability problems of crimp connection devices, it has often become necessary to use mechanical, hand-operated insulation strippers which strip off the insulation by scraping or cutting action. One such device is disclosed in U.S. Pat. No. 4,117,749 (Economu). It is also known to use small, hand-held strippers wherein a plurality of rotating blades driven by, for example, a pneumatic motor, spin around the wire and cut the insulation from a segment thereof.
A more automatic version of the rotating blade stripper is manufactured by The Eraser Company, Inc., of Syracuse, N.Y. In this apparatus, the wire is fed through the center of the machine and advanced through the center of the rotating stripper blades by means of an automatic clamp device which grips the wire and moves it by a predetermined distance. The cutter blades are mounted on individual axes and caused to rock inwardly by means of a cam-like thrust block which is rotating in synchronism with the blades and is pressed axially against complementary cam surfaces on the blades so as to cause them to pivot inwardly. The depth of cut is controlled by adjusting the axial distance through which the thrust block is moved by a pneumatic piston and cylinder.
As disclosed in copending application Ser. No. 175,441, it is also known to mount a wire insulation stripper of the rotating blade type so that feed wire to a coil winding machine passes therethrough. In this case, the feed wire would pass through the stripper apparatus and then to a rotating spindle or flyer on the winding machine, and the stripper will be positioned at a predetermined distance from the wire cutoff device of the winding machine. Attempts have been made to strip wire as it is being drawn into the winding machine by the spindle or flyer, but the linear speeds of the wire are so great that it was virtually impossible to remove all of the insulation on the wire. The insulation was removed in a spiral pattern, which was not suitable for establishing good solder or brazed connections. Furthermore, the speeds were so great that the wire would have a tendency to become caught and break. To alleviate this problem, the wire would be stopped and then pulled slowly through the rotating blades. It is further disclosed in said application to interconnect the wire stripper with the control panel of a conventional winding machine so that the wire could be stopped, the stripper actuated, etc. on certain turn counts. For a given machine, then, the position of the stripped segment of wire could be located precisely between the blades of the cutter without the necessity for intervention by the machine operator.
Some of the problems experienced with the above-discussed prior art techniques are those of wire breakage and inability to control very accurately the depth of cut. Because of the fine diameter of the wire used in many stator coils, it is crucial to remove only the insulation without cutting into the conductive core itself. Not only does an excessively deep cut lower the tensile strength of the wire, but it reduces its current carrying capacity. Wire breaking during stripping was often caused by the wire deviating from the exact center of the blades, and it was found that very accurate wire guiding devices were needed to ensure that the wire did not deviate laterally from the normal path of travel during the stripping operation.
Accordingly, it is a general object of the present invention to provide apparatus wherein enamel coated wire being fed to a coil winding machine has the enamel insulation effectively stripped therefrom along a desired segment of the wire.
It is another object of the present invention to provide apparatus for stripping wire having very thin layers of insulation wherein a very precisely controlled depth of insulation removal is possible so that the current carrying capacity and tensile strength of the stripped segment of wire can be maintained at a maximum for a given wire size.
It is yet another object of the present invention to provide apparatus for stripping a segment of wire being fed to a coil winding machine wherein the length of the stripped segment can be accurately controlled.
It is yet another object of the present invention to provide an apparatus for stripping wire which can easily be incorporated into the wire feed paths of existing coil winding machines.
It is a further object of the present invention to provide apparatus for stripping the insulation off wire by means of rotating blades wherein the wire is maintained very accurately in the center of the blades so as to avoid breaking and deforming the wire.